The Sikorsky CH-53K King Stallion (Sikorsky S-95) is a heavy-lift cargo helicopter designed and produced by Sikorsky Aircraft. The King Stallion is an evolution of the long running CH-53 series of helicopters which have been in continuous service since 1966, and features three uprated engines, new composite rotor blades, and a wider aircraft cabin than its predecessors. It is the largest and heaviest helicopter in the U.S. military. The United States Marine Corps plans to receive 200 helicopters at a total cost of $25 billion. Ground Test Vehicle (GTV) testing started in April 2014; flight testing began with the maiden flight on 27 October 2015. In May 2018, the first CH-53K was delivered to the Marine Corps. On 22 April 2022, it was declared to have passed initial operational capability. Israel has also reportedly ordered the type; other potential export customers include Japan and Germany. Development H-53 background The Sikorsky CH-53 Sea Stallion came out of the US Marine Corps' (USMC) "Heavy Helicopter Experimental" (HH(X)) competition begun in 1962. Sikorsky's S-65 was selected over Boeing Vertol's modified CH-47 Chinook version. The prototype YCH-53A first flew on 14 October 1964. It was designated CH-53A Sea Stallion, delivery of production helicopters began in 1966. The CH-53A was equipped with two T64-GE-6 turboshaft engines, and had a maximum gross weight of . Variants of the original CH-53A Sea Stallion include the RH-53A/D, HH-53B/C, CH-53D, CH-53G, and MH-53H /J/M. The RH-53A and RH-53D were used by the United States Navy for minesweeping. The CH-53D had a more powerful version of the General Electric T64 engine, used in all H-53 variants, and external fuel tanks. The US Air Force's HH-53B/C Super Jolly Green Giant were for special operations and combat rescue. The Air Force's MH-53H/J/M Pave Low were the final twin-engined H-53s, and had extensive avionics upgrades for all-weather operation. In October 1967, the USMC issued a requirement for a helicopter with a lifting capacity 1.8 times that of the CH-53D, that could fit on amphibious assault ships. Before this, Sikorsky had been working on an enhancement to the CH-53D, under the company designation "S-80", featuring a third turboshaft engine and a more powerful rotor system. Sikorsky proposed the S-80 design to the Marines in 1968. The Marines considered this a good, quick solution, and funded development of a testbed helicopter. Changes on the CH-53E also included a stronger transmission and a fuselage stretched .